1. Field of the Invention
The present invention relates generally to filters for simultaneous removal of suspended solids and solids dewatering, and more particularly to a filter having a particular filter bed construction and an automatic scraper for removing filtered sludge from the filter bed.
2. Description of the Prior Art
Steel processing and treatment facilities produce large quantities of by-products, some of which may present serious disposal problems, while others can be recycled in various ways. One particular steel treatment process involves the fabrication of carbon steel rod into spring wire. In this process, the rod is first cleaned by sulfuric acid prior to being drawn to the proper size. Depending on the initial and final gage, some of the drawn wire may be heat treated, recleaned and drawn again to the final dimensions.
In a typical treatment sequence, coils of wire are submerged in a tank containing sulfuric acid for sufficient time to remove scale and dirt. Following the sulfuric acid treatment, the wire coils are subjected to a high pressure water rinse and submerged in a tank containing water to insure complete removal of the acid from the steel rod. In some operations, it has been found desirable to use hydrochloric acid rather than sulfuric acid to remove scale and dirt from the steel rod. In either event, the resulting rinse water contains substantial quantities of dissolved iron.
When it is determined that the acid content of the rinse water has reached a particular concentration, the waste water containing sulfuric or hydrochloric acid is pumped to a neutralization tank and neutralized by sodium hydroxide, lime or the like, which reacts with the acid to form calcium sulfate, sodium sulfate, sodium chloride, calcium chloride, ferrous hydrate, ferric hydrate, magnetite, or other types of dissolved materials.
In general, disposal of this waste water containing sludge has met with some difficulty. For example, the high water content of the sludge, due in part to the ferrous and ferric hydrate, makes the sludge extremely difficult to handle and transport. Furthermore, the water content of the sludge has generally not been recovered by prior art processes, and hence is not available for reuse.
Prior art workers have suggested utilizing settling or clarifier tanks where the sludge settles to the bottom of the tank and is subsequently pumped to a vacuum filter. This method has not been entirely satisfactory because the consentrated sludge particles generally are not sufficiently agglomerated to be effectively removed by the vacuum filter.
It has also been suggested to utilize filter beds with permeable filter material to separate the sludge from the waste water. However, known types of permeable filter beds are inadequate to handle the types of sludge experienced with these steel treatment processes. For example, in filter beds utilizing small smooth sand particles, the filter becomes compacted rather easily and long times are required for draining the water from the sludge. If the smooth sand particle size is increased to increase the rate of water flow, the small sludge particles soon fill the voids between the sand particles and plugging results. Thus the filter bed must be renewed periodically by either removing a significant portion of the filter material or by backwashing the filter bed to open up the filter material. In either event, the sludge resulting from the operation still contains a significant water content, which is subject to the same disposal problem discussed hereinabove.